Improvement of energy usage efficiency via waste heat recovery using thermoelectric modules is a very important topic. Thermoelectric modules are usually composed of arrays of devices, and there are thus many joints in the modules. Indium is ductile and has a low melting point. Transient liquid phase bonding using indium is a potential joining technique for thermoelectric modules which cannot be joined at very high temperatures but need to be operated at relatively high temperatures. The interfacial reactions at the Cu/In/Co and Cu/In/Ni contacts are examined at 200oC and 350oC. At the Cu/In contact, Cu11In9 phase is formed when reacted for 24 hours at 200oC, but Cu2In and Cu7In3 phases were formed at 350oC. A ternary compound is also noticed. Only CoIn3 is formed at the In/Co contact at both 200oC and 350oC. The reaction paths are illustrated using the Co-Cu-In and Cu-In-Ni isothermal sections at both 200oC and 350oC.